The original lore on Sargeras was only that he was a daemonlord trying to corrupt the Council, right? That's still pretty much true even with the expanded lore he's gotten since.

No, it was that the Draenei and Eredar were two entirely separate species (basically broken were Draenei). Sargeras went around locking up demons, and ran into Eredar, who were so evil that after he locked them up he started to doubt his actions and the plans of the Titans. Eventually he had a complete mental break and let all of the demons he previously imprisoned and used them to undo all of his previous work and all work the Titans had ever done. That's why the Sargeras retcon still lingers around and will never be forgotten. There was no twist, or slight misinterpretation of previous lore, it completely changed the order of events, changed the relation of various species and changed motives for a lot of things. The worse part was that it wasn't some obscure portion of lore, it was something that Metzen had written in the WC3:RoC manual. Some argue years after the fact that the lore is stronger because of the retcon, but the original lore was never really given a chance to actually get fleshed out so there is really no ground for that kind of statement.

edit: That being said, it's perfectly explainable for Pandarens to pick up druidism. Their general mentality supports the druidic philosophies of balance, and protecting the land to preserve it for later generations. Their connection with what are most likely their variation of ancients (the celestials), easily puts them on par with the various orders of druid. So what if Cenarius didn't teach them directly during the 10,000 years post-sundering. They line up just fine with it now, and since Blizzard has no issues rewriting things to make stuff convenient in the present, they can write, "Oh, Cenarius taught pandaren when he also taught tauren, but the mogu enslavement made them forget, lulz."

No, it was that the Draenei and Eredar were two entirely separate species (basically broken were Draenei). Sargeras went around locking up demons, and ran into Eredar, who were so evil that after he locked them up he started to doubt his actions and the plans of the Titans. Eventually he had a complete mental break and let all of the demons he previously imprisoned and used them to undo all of his previous work and all work the Titans had ever done. That's why the Sargeras retcon still lingers around and will never be forgotten. There was no twist, or slight misinterpretation of previous lore, it completely changed the order of events, changed the relation of various species and changed motives for a lot of things. The worse part was that it wasn't some obscure portion of lore, it was something that Metzen had written in the WC3:RoC manual. Some argue years after the fact that the lore is stronger because of the retcon, but the original lore was never really given a chance to actually get fleshed out so there is really no ground for that kind of statement.

edit: That being said, it's perfectly explainable for Pandarens to pick up druidism. Their general mentality supports the druidic philosophies of balance, and protecting the land to preserve it for later generations. Their connection with what are most likely their variation of ancients (the celestials), easily puts them on par with the various orders of druid. So what if Cenarius didn't teach them directly during the 10,000 years post-sundering. They line up just fine with it now, and since Blizzard has no issues rewriting things to make stuff convenient in the present, they can write, "Oh, Cenarius taught pandaren when he also taught tauren, but the mogu enslavement made them forget, lulz."

Oh, that change. Not really Sargeras lore but Draenei/Eredar lore. He was still a Titan that fell to form the Burning Legion. As for that enslavement thing made them forget that still doesn't answer how the player character Pandaren pick up Druidism when no one on the Wandering Isle has any clue as to what Druidism even is.